1. Field of the Invention
The present invention relates generally to a MOSFET device and its fabricating method and, more particularly, to a scaled MOSFET device and its fabricating method.
2. Description of Related Art
The metal-oxide-semiconductor (MOS) field-effect transistors including n-channel MOSFET and p-channel MOSFET in CMOS integrated-circuits are scaled very rapidly based on the known scaling rule in order to gain densityxe2x80xa2speedxe2x80xa2power product. Basically, the surface dimensions of a device including device channel length and device channel width can be directly scaled by an advanced lithographic technique, and the device isolation and contact areas must also be scaled accordingly in order to increase the packing density of integrated-circuits. However, as a gate length of a MOSFET device is further scaled down below 0.13 xcexcm, there are several important issues encountered: a larger tunneling current between the channel and the elongated conductive-gate layer near the trench corners in the channel-width direction; a larger tunneling current and a larger overlapping capacitance between the elongated conductive-gate layer and the lightly-doped source/drain diffusion regions; a higher source/drain parasitic capacitance due to the pocket or halo implant; a poorer subthreshold slope or off leakage current due to the improper profile being formed under the gate region; and a contact integrity for shallow heavily-doped source/drain diffusion regions. These issues become serious as the gate length is scaled down below 0.13 xcexcm and the gate-oxide thickness is smaller than 25 Angstroms.
Several methods had been proposed to improve or alleviate a part of the issues as described above. U.S. Pat. No. 5,966,615 had described a process for forming a shallow-trench-isolation (STI) structure to eliminate the larger tunneling current between the channel and the elongated conductive-gate layer near the trench corners in the channel-width direction; however, the active region of a device is reduced by the formed oxide spacer. U.S. Pat. No. 5,614,430 had proposed a process for forming a MOSFET device with an anti-punchthrough ion-implantation through an opened gate region to reduce the parasitic source/drain junction capacitances due to the pocket or halo implant; however, the other issues as stated are overlooked and the process steps for forming a MOSFET device are critical for practical applications. U.S. Pat. No. 5,856,225 had described a process for forming a MOSFET device with a self-aligned, ion-implanted channel region after forming the source and drain diffusion regions; however, the shallow-trench-isolation (STI) used, which is similar to that used in U.S. Pat. No. 5,966,615, is difficult to eliminate a larger leakage current between the channel and the elongated conductive-gate layer near the trench corners in the channel-width direction and a larger tunneling leakage current and a larger overlapping capacitance between the source/drain diffusion regions and the elongated conductive-gate layer through the overlapping area. Moreover, the metal-silicide layer formed over each of the heavily-doped source/drain diffusion regions is experienced by several thermal cycles such as the gate-oxide formation, the poly-gate formation, and the poly-gate silicidation and the integrity of the source/drain contacts becomes a major issue. U.S. Pat. No. 5,955,759 had described the elevated conductive layers over the source/drain diffusion regions by using a selective epitaxy technique to reduce the contact resistance for shallow source/drain junctions; however, the high parasitic capacitances between a T-shaped gate and the elevated source/drain conductive layers become a drawback for a high-performance MOSFET device.
It is, therefore, an objective of the present invention to offer a scaled MOSFET device and its fabricating method for eliminating and alleviating the issues encountered.
Accordingly, a scaled MOSFET device and its fabricating method are disclosed by the present invention. The scaled MOSFET device of the present invention comprises a shallow-trench-isolation structure for eliminating the tunneling leakage current between the channel and the elongated conductive-gate layer near the trench corners in the channel-width direction; a self-aligned source/drain diffusion structure with a buffer-dielectric layer to reduce the overlapping area between the elongated conductive-gate layer and the lightly-doped source/drain diffusion regions and an offset region for forming self-aligned source/drain silicidation contacts; and a highly conductive-gate structure having a pair of second conductive sidewall spacers for forming an implant region in a central portion of the channel for eliminating the parasitic source/drain junction capacitances and alleviating the hot-electron reliability and the punch-through effect.
The shallow-trench-isolation structure of the present invention comprises a first conductive layer over a gate-dielectric layer being formed over a channel region and the first raised field-oxide layers being formed in a shallow-trench-isolation region under the elongated conductive-gate layer. The self-aligned source/drain diffusion structure comprises a buffer-dielectric layer being formed over each sidewall of the gate region and on each side portion of the gate region for forming lightly-doped source/drain diffusion regions; a first sidewall dielectric spacer being formed over each sidewall of the buffer-dielectric layers for forming the heavily-doped source/drain diffusion regions; and a second sidewall dielectric spacer being formed over each sidewall of the first sidewall dielectric spacers to define the self-aligned source/drain silicidation contacts. The highly conductive-gate structure comprises a pair of second conductive sidewall spacers being formed over the inner sidewalls of the gate region and on a portion of a flat surface formed by the first conductive layer and the first raised field-oxide layers for forming an implant region in a self-aligned manner; and a composite conductive-gate structure including a salicide-gate structure and a polycide-gate structure being formed over the flat surface formed by the first conductive layer and the first raised field-oxide layers.